Fan antenna with tail



Aug. 3, 1948.

A. S. MEIER FAN ANTENNA WITH TAIL Filed Dec. 4, 1944 Patented Aug. 3, 1948 FAN ANTENNA WITH TAIL Allen S. Meier, Xenia, Ohio, assignor to United States of America as represented by the retary of War Sec- Application December 4, 1944, Serial No 566,631 a (Granted under the act of March a, 1883, as

amended April 30, 1928; 370 0. 757) 1 Claim.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me, of any royalty thereon.

This invention relates to antennas and more particularly to a broad-band wire antenna.

The term fan antenna, as conventionallyused, is applied to a wire antenna that is substantially of a trianuglar shape and wherein the triangle base line wire terminates at its intersections with the triangle side line wires.

The objects of the present invention comprise the provision of an improved wire antenna of a desired geometrical shape, such as a triangle or the like, that hasbroadband characteristics; a wire antenna that simulates a large radiating surface without sacrificing the general impedance characteristics of a solid conductor; a wire antenna wherein the lengths of at least one wire may be altered to, control the impedance of the antenna without materially affecting the radiation characteristics thereof; and a wire antenna wherein a base line wire extends beyond its intersection with laterally disposed wires for a sufiicient distance to match the input impedance of a coaxial cable thru which the antenna is fed.

With the above and other objects in view which will be apparent to those who are informed in the antenna art from the following description, an illustrative embodiment of the resent invention is disclosed in the accompanying drawing wherein the figure is aside elevation of a plane fuselage with an antenna that embodies the present invention mounted thereon.

The fan antenna that has been chosen as being illustrative of one embodiment of the present invention comprises a single wire or individual wires, as preferred, that describe a geometrical figure, such as the triangle shown or the like. The antenna shown comprises a triangle that has a pair of'sides l and 2 that converge at a point 3, and a base 4 that connects the sides I and 2 at their ends remote from their point of convergence 3 and that continues to provide a tail 5.

The convergence point 3 of the antenna sides I and 2 may also be an attaching point for a desired number of additional wires 6 that form parts of the antenna, as by extending across the antenna so that their ends remote from the convergence point 3 are attached to the base 4, or the like. The convergence point 3 also provides a desirable connection for the antenna to which a coaxial cable, not shown, or other suitable connector may be attached with the central conductor of the coaxial cable connected with 1 2 the antenna and with its outer conductor grounded to the skin of aeroplane In, or other desired mounting for the antenna inside of which aeroplane II) the coaxial cable is disposed. An insulation plate I I provides a mounting for an antenna connector, not shown, at the antenna convergence point 3. a n 1 The antenna is supported in any desired man ner, as by means of an insulator l5 at the remote end of the antenna tail 5 and an insulator 16 at the junction of the antenna side 2 with the antenna base 4, or the like. Resilience is preferably impartedto the mounting in any desired manner, as by having a desired type of spring l'l interposed between the insulator i5 and a securing means Iii-that is attachedto a slipport, such as the fin l9 of the-ship Ill or the li e.

Th antenna wires are preferably. maintained substantially taut in any suitable way, as by means of a cable 20 that has one end attached to the antenna insulator, l6 and that passesthru a guide 2| on the top of a strut or antenna mast 22 and that continues over a pulley or the like, not shown, in a housing 23 mounted in the fuselage of the plane ID. The cable 20 is attached in any desired manner within the plane fuselage.

In operation, the antenna that formsthe subject matter of the present invention is adapted for use where a simple antenna isneeded for broad-band application. The antenna is operated at a substantially high impedance level. The length of the antenna tail 5, in its relation with the dimensions of the remainder o ffthe antenna, controls the input impedance of the antenna. An illustrative installation of the antenna indicates that wherethe impedance level of the antenna is ohms, the standing wave ratio of the antenna is less than 2 to 1 for the transmission of signals within, the wavelength range of from 18.5 to 28 megacycles.

Transmitting equipment such as those known in Britain as the Jostle jamming equipment transmitter works over a band of frequencies that requires an antenna system that has a constant input impedance over the entire band of frequencies in order that maximum eiliciency may be obtained. The required broad band characteristics may be obtained by an antenna with a large radiating surface such as a large cylinder, cone or similar shape. This type of antenna, however, is not adapted for use at low frequencies on aircraft because of their large dimensions, which make the antenna objectionably conspicuous and impractical for tactical reasons as Well as being aerodynamically unsatisfactory.

The fan-shaped array of a plurality of wires such as form the antenna that is contemplated hereby, simulates a large radiating surface Without the sacrifice of the-.needed:;impedance characteristics that are provided by a solid conductor. In some installations three wires have been successfully used for an antenna that has a limited band width without exceeding a desired standing wave ratio of 2 to 1 owing to-the impedance mismatch over the band. 1

In the present illustrative antenna, the antenna wires 4 and serve asamecham'cal .continuation of the cable to support the remaining wires and parts of the antenna. The wires,

I and 2 are flared preferably atsubstantially The base wire 4 and tail 5 section, of theantenna increases the electrical length of the antenna and is an effective methodfor controlling the impedance thereof without impairing its radiation characteristics. The insulation ofthe supporting cable 20"from'- the base wire 4' and tail 5 section of the antenna serves-to prevent coupling to the supporting cable 20 which destroys the electrical characteristics of the antenna. The antenna preferably is fed through-the skin of the ship I Dby meansof an amphenolconnector base, not shown, on the-inside'of the fuselage and a ceramic lead-in insulator I I that" is disposed on the outside of the fuselage.-

In flight the antenna has proved very stable and produces negligible drag on the aircraft. The supporting cable ZB preferably ismounted by means of conventionally used brackets 18 that are" provided for an original communication antenna; The antenna mounting may be modified so that thepresent antenna may extend from the antennamast 22to' the wingtips, or otherwise,- as desired.

It has been found that; the Jostle type of transmitter workedmost efficiently into a high impedance loadof the order of 150" to 200 ohms with an antennathatwas designed to operate at anti-resonance 'nearits mid-band andwherein the wires4 and 5' totalled l'lfeet and the wires la'nd"2 were each 'l' feet' in length. The transrnitter is preferably'mounted very close to the antenna feed point so that a short length of high characteristic impedance coaxial cable, not shown, may be used between the transmitter and the antenna.

Field patterns on this type of antenna have been obtained at 24 megacycles in-the vertical planes for-every 30 around the ship as in the horizontal plane on the horizon.

Maximum signalstrength with vertical polarization occurs forward of the ship with a null occurring approximately 30"- downward from the horizon. Optimum horizontal polarization occurs upon the antenna side of the aircraft as would be normally expected. With an antenna that embodies the present invention, ranges up to 25 miles were covered in tests and for any given range the signal magnitude was constant over the. entire. frequency band. I

Using the: accepted standard of a2 to 1 standing wave ratio as a satisfactory broad antenna for purposes of jamming, experimental antennas that embody the present invention have been found to have a useful band width of from 18.6 to 28 megacycles which represents a 40% band width. The antenna, as designed for a 20 to 27 megacycle range, is within the accepted limits and the standing wave ratio varies from 1.5 to 1.8 over the band.

It is to be understood that the antenna that forms the subject matter of the present invention, ofxwhich the illustrative antena that has been shown and described herein is an example, has been submitted for the purposes of illustrating and describing the present invention and that suitable modifications and substitutions may be made in the parts andassembly thereof without departing from the present'invention -as defined by the appended claim.

What I claim is:

A broadband unsymmetricalwire antenna connected to an input'means of predetermined impedance, comprising a-basewir'e, av plurality of spaced side wires connected -at their spaced ends to said base wire and converging away from their spaced connections with-said base wire, a convergence point atwhichsaid side wiresjoineach other, and are electrically connectedto saidinput means, and a tailportion -making said antenna unsymmetrical by extending from one end only of said base wireand said tail portion being of a predetermined lenth-andf imparting to said antenna an impedance value that sub stantially matches the characteristic impedance of said input means to'which the antenna side wires maybe connected at theirconvergence point. 1

ALLENS. MEIER REFERENCES CITED The followingreferencesare of. recordin the fileof this patent t,

UNITED STATES l PATENTS Name Date De Forest et al; Jan. 19,1904

De Forest Jan. 3.0,,191'7 Wells" May2, 1939 OTHER REFERENCES" Principles Underlying. Radio Communication; (second% edition), RadioyCommunication Raine phlet' No; 40,-,rev-ised to; May 24,-, 1921, Signal Corps, U. S. Army, page 306: .Copy inDiv; 5.1.

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